DESCRIPTION: The first level of DNA organization in eukaryotes resides in the nucleosome, which consists of approximately 200 bp of DNA wrapped around the histone octamer. The nucleosome is regarded as the most fundamental element of chromosomal structure. Incorporation of other proteins into oligonucleosomal arrays gives rise to specific chromatin structures capable of specific nuclear functions such as transcriptional activity. The general goals of the proposed research are to identify and characterize the structural and functional states of nucleosomal arrays and to understand the role of histones, linker histones, and transcription factors in directing and maintaining higher order chromatin structures brought about by nucleosome array folding and self- association. Three specific tasks are proposed to address the hypothesis that the intrinsic conformational dynamics of nucleosomal arrays contribute to formation of the 30 nm chromatin fiber and higher chromosomal domains, and that folding provides a barrier to RNA polymerases that can be modified by other proteins such as H1 to achieve specific states of transcriptional activity. These studies are expected to provide the baseline necessary to attain the goal of assembling transcriptionally active and repressed chromatin states in vitro from pure components.